The study on the threshold strain of microvoid formation in TRIP steels during tensile deformation

Transformation Induced Plasticity (TRIP) steels exhibit a better combination of strength and ductility properties than conventional high strength low alloy (HSLA) steels, and therefore receive considerable attention in the automotive industry. In this work, the tensile mechanical behaviors of TRIP-aided steels were studied under the condition of the quasi-static and high deformed rates. The deformed specimens were observed by scanning electron microscope (SEM) along the tensile axis. The threshold strain of microvoid formation was examined quantitatively according to the evolution of deformation. The results showed that: the yield and tensile strengths of TRIP steels increase with the strain rate, whereas their elongations decrease. However, the threshold strain for TRIP steels at high strain rate is larger than that at low strain rate. Comparing with the deformed microstructure and microvoids formed in the necking zone of dual phase (DP) steel, the progressive deformation-induced transformation of retained austenite in TRIP steels remarkably increases the threshold strain of microvoid formation and furthermore postpones its growth and coalescence.